acoustic placement/small bright room

Small rooms require much more damping than larger rooms. You actually can't have as long a reverberation time in small room as in large room without this ill effect you've experienced. This is because for the same reverberation time there are many more reflections and paths that cross the listener. The result is a very muddied and unclear sound. It's also not just in the high frequency--that's where you've heard it the worst, but it carries down in to the midrange as well. Then what can be worse is what happens to the bass--you can get severe bass build up in small rooms. If your dimensions are good--in the right ratios, then your problem will be minimized, but if they aren't, then you will have another issue to deal with.

My guess is that your drapes are not overkill, but they probably have a low absorption coefficient relative to pressed fiberglass. Thus you will need a lot more quilt surface area than fiberglass.

You're correct in figuring it's your room, it usually is. You can try to get the speakers positioned so that they crossfire in front of you a couple of feet. Also some bass traps can help. These aren't cheap but will help significantly and can be inexpensive if you build them yourself. Go over to AA and search for a Jon Risch DIY bass trap. Another possibility is either digital or analog equalization. This can help more than hurt in many situations. As a matter of fact I've no doubt that most audiophiles are listening to sound that isn't near their systems potential because of room acoustics. Being as you can get away with quilts on the walls you should invest in some at least 3" or 4" wedge foam and do it right. The foam will absorb down to much lower frequencies (250-500 for the 3") You can just use spray adhesive to hold it up. Do your entire front wall behind your system. Both side walls about 4' out and the ceiling the same as the walls. Last possiblity is get speakers with pots for the tweeters.

"they probably have a low absorption coefficient relative to pressed fiberglass."

Pardon the tangent, but could you please tell me if this extends to polyfill? If I am not mistaken it is used in quilts.